Circularly polarized antenna



March 21, 1961 A. KAMPINSKY 2,976,534

CIRCULARLY POLARIZED ANTENNA Filed July 2, 1959 22 FIGJ N l .2 J A N l l 3 DIRECTION OF POLARIZATION ENERGIZING l 26 TR-l C'RCUT, F563 DIRECTION OF POLARIZATION INVENTOR ABE KAMPINSKY ENERGIZING/ CIRCUIT 2 BY j iazr ORNEY (IlRCULARLY POLARIZED ANTENNA Abe Kampinsky, Belmar, N.J., assignor to the United States of America as represented by the Secretary of the Army Filed July 2, 1959, Ser. No. 824,756

4 Claims. (Cl. 343-756) (Granted under Title '35, [1.5. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

This invention relates to antenna systems and more particularly to antennas which are adapted to radiate and receive circularly polarized wave energy.

In pulsed radar systems it is sometimes desirable to transmit circularly polarized waves. When, however, a circularly polarized wave of one screw sense is transmitted and strikes a highly conducting smooth surface, the reflected wave will have the opposite screw sense. One or: the problems of such a system is to provide some means to receive and detect the opposite screw sense with a common antenna arrangement. One well known arrangement for producing circularly polarized waves consists of two orthogonally arranged dipole antennas each of which is provided with balanced dipole element currents by utilizing discrete pairs of mutually opposing longitudinal slots in the outer conductor of a coaxial feed line system. The longitudinal slots provide the means for producing balanced currents from the unbalanced coaxial line, a technique which is well known in the art. In such a system it is possible to reverse the screw sense by interchanging the relative positions of the orthogonally polarized dipoles with respect to the slots. However, this is not feasible for high speed operation as would be required for radar operation. Also, in the radar countermeasures systems it is desirable to rapidly reverse both the transmitted and received screw sense.

It is an object of the present invention to provide a circularly polarized antenna arrangement wherein rapid switching from one circularly polarized screw sense to the opposite circularly polarized screw sense is achieved for both transmitting and receiving.

It is a further object of the present invention to provide a circularly polarized antenna arrangement adapted to transmit circularly polarized waves in one screw sense and to receive circularly polarized waves according to the opposite screw sense.

In brief, there is provided an antenna system which includes a coaxial feed line having an outer conductor with four longitudinal slots therein at substantially equal angular intervals to form a first and a second pair of opposing inter-slot portions. Also included is a first dipole antenna having each of its elements extending radially outward from a respective inter-slot portion comprising said first opposing pair and a second dipole antenna spaced 90 degrees physically from the first dipole and coplanar therewith. Each element of the second dipole antenna extends radially outward from a respective inter-slot portion comprising the second opposing pair. In addition, there is included switch means for simultaneously short-circuiting either pair of mutually opposing slots. With one pair of mutually opposing slots short-circuited, one screw sense of the circularly polarized wave is established. When the other pair of mutually opposing slots are short-circuited, the phase quadrature currents fed to the dipole elements are reversed so that 2,976,534 Patented Mar. 21, 1961 the screw sense of the circularly polarized wave is reversed in space.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a perspective view of the antenna;

Fig. 2 is a section taken along the lines 22 of Fig. 1;

Figs. 3 and 4 illustrate the respective screw sense of circular polarization when each of the opposing slot pairs are short-circuited; and

Fig. 5 illustrates electronic slot-shorting means for the antenna shown in Fig. 1.

Referring now to Fig. 1 of the drawing, at 10 there is shown a coaxial feed line having its outer conductor 12 terminated in four longitudinal slots 14, 16, 18, and 20, spaced at substantially equal angular intervals around the periphery of the outer conductor. The slots 14 and 16 are diametrically opposed as are the slots 18 and 29, the length of each slot being one-quarter wavelength of the operating frequency. Afiixed to oppositely disposed inter-slot segments 22 and 24 are paired radiating elements 26 and 28 which constitute a first dipole antenna and afiixed to oppositely disposed inter-slot segrnents 30 and 32 are paired radiating elements 34 and 36, which constitute a second dipole antenna. The two dipole antennas are co-planar and are spaced degrees physically. Each radiating antenna element thus extends radially outward from a respective inter-slot portion and positioned such that each antenna element is centrally positioned with respect to adjacent slots. The respective lengths of the antennas are such that the first dipole antenna comprising the dipole elements 26 and 28 is more than one-half wavelength long while the second dipole antenna comprising the dipole elements 34 and 36 is less than one-half wavelength long. With the longitudinal dimension of the slots at one-quarter wavelength of the operating frequency as hereinabove described, the relative phase of the currents in the orthogonally arranged dipole antennas can be adjusted to provide quadrature relationship and thereby fulfill the requirements for circularly polarized radiated energy. An electrically conductive element 40 connects the inner conductor of the coaxial feed line to any one of the inter-slot segments and is herein shown as being connected to inter-slot segment 22. A rotary type switch 42 is rotatably mounted coaxially Within coaxial feed line 10 and is provided with two insulated radial arms terminated in diametrically opposed arcuately-shaped end conductors as shown at 44 and 46. The arcuate end members of switch 42 are made wide enough so as to respectively short-circuit a mutually opposing pair of slots simultaneously when positioned therebetween, preferably in the plane of the dipoles. Thus, either pair of mutually opposing slots may be short-circuited at any instant, with the remaining pair of mutually opposing slots being open-circuited. The switch 42 may be positioned by manual means or by relay operated means well known in the art. Also, the rotary switch may be replaced by electronic type switches such as TR tubes. With such an arrangement, discrete TR tubes may be connected across each of the slots and a mutually opposing pair of such TR tubes is simultaneously fired at any one instant to provide a short-circuit thereacross, the remaining two TR tubes being maintained in the deenergized state so that its associated slots are opencircuited. The firing of the TR tubes may be synchronized with the radar transmitted pulse so that when transmission occurs, only one opposing pair of TR tubes are energized, and, at the end of the transmitted pulse only the other opposing pair of TR tubes are energized. In Fig. 5, the elements TR-l, TR-2, TR-3, and TR-4 are gas discharge type TR tubes commonly employed in radar systems. A pair of opposing TR elements, TR-l and TR3 for example, may be simultaneously activated or energized in synchronism with the outgoing pulse" of a-radar transmittento provide the respective short circuits for corresponding opposing slots. For recep tion, only the other pair of opposing TRelements is activating. Conventional circuitry well known inthe art may be utilized as: the activating or energizing means. In Fig. such means are represented by respective energizing circuits 1 and 2 which are adaptedv to be triggered by the output of a synchronizing circuit 59 responsive to the output of a transmitter pulse. The energized circuits are arranged such that when the transmitter pulse is present an outputis derivedfrom energizing circuit 1 to ionize TR1 and .TR3.but-no output is derived from energizing circuit 2 so that opposing TR elements TR-Z andTR-4 remain deionized for the duration or" the transmitter pulse. Immediately after the transmitter'pulse, an output is derived from energizing circuit 2 but no output is available from energizing circuit 1 so that during the receiving time-only TR elements TR-2 and TR-4 are energized, and TR elements TR-l and TEL-3 remain deenergized.

In operation, phase quadrature currents are fed to the dipoles which are also physically spaced 90.degrees so that circular or rotating polarization is readily obtained regardless of which pair of opposing slots are shortcircuited. It can be seen that withonepair of mutually opposing slotsshort-circuited in the. plane of the dipoles, one screw sense of the circularly polarized Wave is established. When the other pair of mutually opposing slots is short-circuited, the phase of currents fed to the dipole elements are reversed so that the screw sense of the circularly polarized wave is reversed in space. These relationships are shown in Figs. 3 and 4.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications maybe made therein without departing fromthe invention, and it is, therefore, aimed in the appended claims to cover: all such changes and modifications as fall within thetrue spirit and scope of the invention. 7 i

What is claimed is: V

1. An antenna system comprising a coaxial feedline having an outer conductor with four longitudinal slots therein at substantially equal angular intervals forming a first and a second pair of opposing inter-slot portions, a first dipole antenna having each of its elements extendin radially outward from a respective inter-slot portion comprising said first opposing pair, a second dipole antenna spaced degrees physically from said first dipole antenna and coplanar therewith, each element of said second dipole antenna extending radially outward from a respective inter-slot portion comprising said second opposing pair, and switch means for simultaneously short-circuiting either pair of mutually opposing slots.

2. The antenna system in accordance with claim 1 wherein said first dipole antenna is less than one-half wavelength and said second dipole antenna is greater than. one-half wavelength at the desired operating frequency.

3. An antenna system comprising a coaxial feed line having an outer conductor, with four longitudinal slots therein at substantially equal angular intervals forming a first and a second pair of inter-slot portions, the length of each of said slots being one-quarter Wavelength of the desired operating frequency, a first dipole antenna having each of its elements extending radially outward from a respective inter-slot portion comprising said first opposing pair, asecond dipole antenna spaced 90 degrees physically from said first dipole antenna and co-planar therewith, each element of said second dipole antenna extending radially outward from a respective inter-slot portioncomprising said second. opposing pair, the length of said first and. second dipole antennas being greater than one-half wavelength and less than onehalf wavelength, respectively, at the desired operating frequency, and switch means for simultaneously short-circuiting either pair of mutually opposing slots in the plane of the dipole antennas.

4. The antenna, system in accordance with claim 3 wherein said last mentioned means comprises four TR-type tubes-respectively connected across each of said slots and means for simultaneously energizing one pair of oppositely arranged TR tubes and maintaining the other pair of oppositely arranged TR tubes in the deenergized state.

No references cited. 

